I2C communication protocol with the compass module is the same as popular eeprom's such as the 24C04.. First send a start bit, the module

address (0XC0) with the read/write bit low, then the register number you wish to read. This is followed by a repeated start and the module

address again with the read/write bit high (0XC1). You now read one or two bytes for 8bit or 16bit registers respectively. 16bit registers are

read high byte first. The compass has a 16 byte array of registers, some of which double up as 16 bit registers as follows;

Register 0 is the Software revision number (8 at the time of writing). Register 1 is the bearing converted to a 0-255 value. This may be easier

for some applications than 0-360 which requires two bytes. For those who require better resolution registers 2 and 3 (high byte first) are a 16

bit unsigned integer in the range 0-3599. This represents 0-359.9°. Registers 4 to 11 are internal test registers and 12,13 are unused. Register

14 is undefined. Don't read them if you don't want them - you'll just waste your I2C bandwidth. Register 15 is used to calibrate the compass.

.

Register

Function

0 Software Revision Number

1 Compass Bearing as a byte, i.e. 0-255 for a full circle

2,3 Compass Bearing as a word, i.e. 0-3599 for a full circle, representing 0-359.9 degrees.

4,5 Internal Test - Sensor1 difference signal - 16 bit signed word

6,7 Internal Test - Sensor2 difference signal - 16 bit signed word

8,9 Internal Test - Calibration value 1 - 16 bit signed word

10,11 Internal Test - Calibration value 2 - 16 bit signed word

12 Unused - Read as Zero

13 Unused - Read as Zero

14 Unused - Read as Undefined

15 Calibrate Command - Write 255 to perform calibration step. See text.